. build/envsetup.sh 编译环境中新增命令

- croot: Changes directory to the top of the tree.- m: Makes from the top of the tree.- mm: Builds all of the modules in the current directory.- mmm: Builds all of the modules in the supplied directories.- cgrep: Greps on all local C/C++ files.- jgrep: Greps on all local Java files.- resgrep: Greps on all local res/*.xml files.- godir: Go to the directory containing a file.-------------------其中，mmm 可以单独编译一个应用程序，例如：